Aeration systems are used to prevent spoilage in stored grain, and to reduce the moisture content of the grain. Such systems include a perforated duct located inside the bin, and a fan directing air into the duct, out through the perforations and up through the grain and out through a vent in the roof of the bin. The fan and perforated duct area are sized to provide the desired airflow for the height and volume of grain in the bin. The perforated duct area must be large enough to provide sufficient open spaces so that the required volume of air can flow through the perforations without developing excessive back-pressure.
Providing sufficient perforated area in flat bottom bins is not usually a problem as the duct can be provided by a perforated floor area, or by a horizontal perforated tube or tube network if more perforated area is required resting on the bin. Such systems are also readily placed in flat bottom bins which have access doors at ground level to allow personnel to enter to manually empty the bin.
Hopper bottom bins have a cone shaped floor sloping to a central discharge chute so that all the grain flows down the floor to the chute, and no manual removal is required as in a flat floor bin.
Since the floor of a hopper bottom bin slopes, the length of a horizontal tube network in the hopper is limited. To provide added perforated wall area, vertical tubes with concentric perforated inner and outer walls are commonly used, such as the “Rocket™” vertical aeration systems sold by Edwards Grain Guard of Lethbridge, Alberta, Canada. A transition duct extends through the sloped floor to connect the fan outside the bin to the tube which extends upward in the center of the bin, and air flows out the perforated sides and out the open bottom and upward through the grain in the bin. Grain flows downward along the outer walls and also down through the open center of the tube along the inner walls.
U.S. Pat. No. 7,568,297 to Pierson et al. discloses an aeration duct for a hopper bottom bin that has a pyramid frame in the center of the bin with legs attachable to the sloped floor of the hopper bottom, and sloping concave perforated walls attached to the legs. An air stream is directed into the interior of the frame, and moves out into the grain through the perforated walls.
Canadian Patent Application Number 2,707,941 of Assie discloses an aeration duct for a hopper bottom bin that comprises an enclosed box with an open bottom and louvered top that extends across the cone at the bottom of the bin. Air is directed into the enclosure and then out the open bottom and the louvers along the length of the box and up through the grain.
A problem with hopper bin aeration duct systems is the difficulty of installing them in existing bins. Such hopper bins typically have the discharge opening at the bottom, and a only a relatively small access opening in the sloping floor or the wall above the floor. For example the conventional Rocket™ system must be installed before the bin is installed on the hopper. To address this limitation the manufacturer has developed a Retro Rocket™ where the pieces can fit through the available access holes and be assembled inside the bin. Pierson also claims to be able to install his system in existing bins.